1) Field of the Invention
This invention relates to a commutator-less direct-current motor, the stator of which has a single coil with a plurality of active branches and means to control the current in the coil depending on the winding position of the rotor, and the rotor of which is provided with a permanent magnet.
2) Description of the Prior Art
Motors with electronic commutation are generally known and are used in particular as economical drives for axial and radial fans. As a rule, one or more Hall-effect elements are used to detect the position of the rotor, of the detection uses the back-EMF principle.
Commutator-less direct-current motors of this type are disclosed, for example, in DE-A-2 260 069. In this publication, the embodiment illustrated in FIGS. 1 to 4 shows a commutator-less direct-current motor that has a plurality of discrete coils. In the realization illustrated in FIG. 8 there is only one single coil, which has four active branches 103 to 106 and two essentially inactive coil ends. In this case, the coil has approximately the shape of a drawn-out rectangle. The two coil ends in this case are formed by the facing narrow sides of this rectangle.
EP-A-0 221 459 discloses a small fan with a commutator-less direct-current motor that also has a single coil. In this case, too, the coil of the stator is in the shape of a drawn-out rectangle. The narrow sides of the coil form essentially inactive areas.
The object of the invention is to create a commutator-less direct-current motor of the type described above that has an essentially greater efficiency and can nevertheless be manufactured economically. The direct current motor is suitable in particular for use in a small fan.